A comparative ultrastructural study of hepatocyte nucleolar structures observed in physiological and pathological conditions

Aggregates of fibrillar material were observed within the meshes of the nucleolonema and at the periphery of hepatocyte nucleoli of 7-day-old untreated C3Hf and BUA mice. These aggregates had a lower density and smaller diameter than microspherules induced in mice of the same age and strains by urethane, a chemical that has been shown to inhibit RNA and DNA synthesis. However, aggregates shared some features with the microspherules since both structures had a similar fibrillar appearance and an identical localization, were easily digested by pronase and pepsin, and were bleached more than chromatin after being subjected to Bernhard's preferential staining. A close correlation between aggregates and microspherules is postulated.